Polyacetylene molecular structure

FIGURE 1.2 Electronic and molecular structures of (a) polyethylene and (b) polyacetylene. 

Poly(4-phenoxybenzoyl-1,4-phenylene) (PPBP), sulfonated, 23 718 Polyacetal, antioxidant applications, 3 121 Polyacetaldehyde, 1 103 Polyacetal fiber, 13 392 Polyacetylene, 7 514-515 26 953 conduction in, 7 527 22 208 molecular structure of, 22 211 optical band gap, 7 529t Peierls distortion in, 22 203, 208 room temperature conductivity, 7 532 synthesis of, 22 213... 

Hydroxy-terminated polyester (HTPS) is made from diethylene glycol and adipic acid, and hydroxy-terminated polyether (HTPE) is made from propylene glycol. Hydroxy-terminated polyacetylene (HTPA) is synthesized from butynediol and paraformaldehyde and is characterized by acetylenic triple bonds. The terminal OH groups of these polymers are cured with isophorone diisocyanate. Table 4.3 shows the chemical properties of typical polymers and prepolymers used in composite propellants and explosives.E4 All of these polymers are inert, but, with the exception of HTPB, contain relatively high oxygen contents in their molecular structures. 

The first conducting polymer was trans-polyacetylene which was doped with bromine and was produced at 1970s. Soon other conjugated polymers such as poly (p-phenylene), polypyrrole (PPy), polyethylene dioxythiophene (PEDOT) and polyaniline (PANi) and their derivatives which are stable and processable were synthesized. The molecular structures of a few ICPs are shown in Figurel. 

The earliest band theory calculations for conjugated polymers were focussed on rrans-polyacetylene (t-PAc). It was the first system in which metallic levels of electrical conductivity were observed (Shirakawa et al., 1977) and has by far the simplest molecular structure of this class of polymers. There are two possible structures, either ... 

This review describes the synthesis and properties of polyacetylenes with substituents (substituted polyacetylenes) mainly on the basis of our recent studies At first, Sections 2 and 3 survey the synthesis of substituted polyacetylenes with group 6 (Mo, W) and group 5 (Nb, Ta) transition metal catalysts respectively, putting emphasis on new, high-molecular-weight polyacetylenes. Then, Section 4 refers to the behavior and mechanism of the polymerization by these catalysts. Further, Section 5 explains the alternating double-bond structure, unique properties, and new functions of substituted polyacetylenes. Finally, Section 6 provides detailed synthetic procedures for substituted polyacetylenes. 

FIGURE 1.2. Molecular structure of widely used it-conjugated and other polymers (a) poly(para-phenylene vinylene) (PPV) (b) a (solid line along backbone) and it ( clouds above and below the a line) electron probability densities in PPV (c) poly(2-methoxy-5-(2 -ethyl)-hexoxy-l,4-phenylene vinylene) (MEH-PPV) (d) polyaniline (PANI) (d.l) leucoemeraldine base (LEB), (d.2) emeraldine base (EB), (d.3) pernigraniline base (PNB) (e) poly(3,4-ethylene dioxy-2,4-thiophene)-polystyrene sulfonate (PEDOT-PSS) (f) poly(IV-vinyl carbazole) (PVK) (g) poly(methyl methacrylate) (PMMA) (h) methyl-bridged ladder-type poly(jf-phenylene) (m-LPPP) (i) poly(3-alkyl thiophenes) (P3ATs) (j) polyfluorenes (PFOs) (k) diphenyl-substituted frares -polyacetylenes (f-(CH)x) or poly (diphenyl acetylene) (PDPA). 

Recent evidence indicates that the influence of molecular structure on gas permeation through polymers is complex. For example, reports investigating series of structurally varied polyimides (5-7), polyacetylenes (2), polystyrenes (2) and silicone polymers (12) show that gas transport rates within a particular polymer class can vary dramatically depending upon the structure of the monomer present. These observations on materials where the monomer changes while the functional "link" remains constant suggest that structural factors other than the polymer class are significant in determing gas transport properties. 

From the viewpoint of its molecular structure, PPV can be considered an alternating copolymer of the repeat units of polyacetylene and poly(p<7r<7-phenylene) (Figure 1.35). With respect to electronic structure, it is one of the simplest non-degenerate ground state polymers, and as such it is attractive for theoretical approaches. 

Figure 8.1 Conformational changes of molecular structure, (a) photoisomerisation of azobenzene, (b) and (c) extension and contraction of polyacetylene and polyaniline, respectively, upon oxidation and reduction...

Figure 2.1 Polyacetylene film with metallic luster (a) and molecular structures (b).

The interest in organic metals is largely due to opportunities for their practical application instead of common materials in electronics, optics, batteries, and other areas. The typical representative of the polyconjugated organic polymers is polyacetylene (PA). Because of the simplicity of its preparation and molecular structure, PA may be considered a prototype for the whole class of organic metals. It became a basic model for the verification of modem concepts of conductivity [2-9]. 

A group of new amphiphilic macromolecules comprised of hydrophobic polyacetylene backbone and hydrophilic pendant groups of naturally occurring species such as amino acids, saccharides, and nucleosides are synthesized. The polymers exhibit solvatochromism. The macromolecular chains show helical confommtions that depend on the molecular structures of the pendants, solvent, temperature, pH, and additives. 

Chart 1. Molecular structures of polyacetylenes containing amino acid moieties. 

The structural orientation is an important factor in order to achieve high conductivity in polyacetylene, and thus increase the hopping probability. Orientation of the polymer chains can be obtained by different methods. In the case of (CH), attempts to orient the fibrillar films by uniaxial extension have resulted in the orientation of the fibrils alone without appreciably changing the molecular structure [16]. 

With these contrasts in molecular structure, morphology and crystallinity between poly-1,6 and polyacetylene, we undertook a study of the oxidation (doping) of poly-1,6 to a conductive state. Indeed exposure to iodine vapor in vacuo at room temperature successfully raised the onductivity from an initial value of 10 s/cm to 10 to 10 s/cm over the period of one hour, a rate similar to that of polyacetylene. However, the conductivity-time curve proceeded through this maximum value and then decreased by about a factor of 10 before plateauing (Figure 1). 

Figure 5 (a) Molecular structure of polyacetylene showing bond... 

Figure 14.44. Molecular structure of a diblock copolymer used as precursor for constructing polyacetylene LB films.

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